There are a number of applications in which construction of a stereoscopic hologram from one or more two-dimensional images is desirable. For example, the structure of an organic molecule can be more fully appreciated when the molecule is shown as a three-dimensional image.
It is particularly useful to provide a hologram of a two-dimensional image generated by a computer. Objects generated by a computer can be more fully studied when viewed in three dimensions, and holograms often serve as an effective yet less expensive alternative to the construction of models. They also facilitate interaction with and manipulation by the user.
Two-dimensional images can not be directly recorded on a holographic plate from typical computer screens which emit their own light, usually from a cathode ray tube screen. Because an object must be illuminated by an object beam of coherent radiation during construction of a hologram, a substitute image of the object, such as a photograph, must first be provided to portray the image.
A multiplex hologram is a hologram containing many narrow strips of holograms, each strip carrying a slightly different view, spacially or temporally, of an object to be displayed. By moving the hologram relative to the viewer, the different perspectives of the object are seen as if a three-dimensional object were present, or as if the object were changing over time.
Presently, to develop a multiplex hologram from a computer screen having a cathode ray tube, a photograph must be taken of the screen for each perspective of the object portrayed on the computer screen. Typically, more than one thousand perspectives, and therefore more than one thousand separate photographs, are required to satisfactorily construct a multiplex hologram. Each photograph must be developed as a print from a negative. In addition to the time and expense involved in developing the large number of prints, the quality of the prints may vary depending on the consistency of the chemicals during the lengthy development period. Each print must be carefully positioned on a holographic table in front of a holographic plate. After the image on that print is recorded, the next print must be carefully positioned and recorded, and so on for more than one thousand prints. Because holograms are established by interference patterns, the slightest vibration on the holographic table interferes with construction of the hologram. A substantial period of time, often as long as ten minutes, must elapse between each repositioning of the next print to allow the holographic table to settle.
In addition, successive portions of the holographic plate must be successively exposed and then masked to record the successive images. Typically, a mechanical sliding slit is positioned in front of the holographic plate to be exposed. Further vibrations are generated when the slit is repositioned.
One system generates a hologram by processing an electronic signal, such as from a video camera. For each of the series of samples of a video signal, the signal is modulated into an information beam whose phase is modified relative to a reference beam. However, the image must be scanned line-by-line and separately modulated for each pixel. In other words, the entire image can not be recorded from the video camera in a single operation.